Piper Jaffray analyst Gene Munster believes that a September launch of the iPhone 5 could add six to 10 million iPhone sales to Apple's Q4.

Apple is expected to unveil its sixth-generation iPhone (dubbed iPhone 5) at a special 12 September event, and will begin shipping on 21 September. The timing of the launch could save Apple from the disappointing fourth fiscal quarter of 2012 that Wall Street is expecting, because all iPhone sales made up until 29 September will count towards Apple's Q4 revenue.

Fortune reports that, on Wednesday, Munster wrote in a note to clients: "We believe that a September launch could result in the final 10 days of the month generating 6-10 million iPhone 5 unit sales, which would likely shift out of December."

"We believe if iPhone 5 launches in September, Apple could sell 26-28 million units in the quarter (this takes into account iPhone sales slowing dramatically from September 12-20, which is announcement to availability)," Munster continued. "This would imply 8% upside to the Street's current $35 billion revenue and 12% upside to EPS of $8.46."

Munster thinks that Apple will sell 27.19 million iPhones in quarter four, up from the Street's estimation of 23 million. He does note, however, that he may reduce his estimate of 49 million iPhone sales in the December quarter (fiscal Q1 2013).

"While predicting the timing of the iPhone release is topical fro investors, we continue to believe that whether iPhone 5 launches in the September or December quarter is largely irrelevant to the overall story, which we believe is that the new phone will be the largest consumer electronics product upgrade in history," Munster concludes.

Rumors suggest that Apple could also launch an iPad mini and an update to its iPod touch at the September event.